The present invention relates generally to valve systems, and, more particularly, to valve systems for use with viscous clutches to reduce “morning sickness” effects.
Viscous clutches are used in a wide variety of applications, such as for automotive fan drive applications. These clutches typically employ relatively thick silicone oil (more generally called shear fluid or viscous fluid) for the selective transmission of torque between two rotatable components. Engage or disengagement the clutch is made possible by selectively allowing the oil into and out of a working area of the clutch located between input and output members (e.g., between a rotor and a housing) where a viscous shear coupling can be created by the oil to transmit torque from the input member to the output member. A valve is used to control the flow of the oil into and/or out of the working area. Some recent clutch designs allow the oil to be stored in a reservoir attached to an input (e.g., a rotor located inside the housing and generally accepting a torque input at all times) while the clutch is disengaged, in order to keep kinetic energy available in the oil to allow rapid engagement of an outer output housing of the clutch from the disengaged/off condition, and to allow the clutch to have a very low output speed (e.g., fan speed) while the valve is positioned to obstruct oil flow into the working area.
One problem experienced with the use of viscous clutches is so-called “morning sickness” (also referred to by other terms such as “fan boom”, “attendant rotation”, etc.). When clutches are at rest when a motor is powered off (e.g., when on a vehicle that has been unused overnight), shear fluid can migrate from the reservoir to the working chamber. The degree of fluid migration to the working chamber often varies depending upon a rotational orientation of the clutch when at rest. In some rotational orientations, bores or other passageways within the clutch are at or near a lower portion of the clutch where gravity can urge significant amounts of the shear fluid through those bores or other passageways and into the working chamber. Upon startup of the motor, rotational input to the clutch can produce a significant degree of undesired engagement of the clutch output, due to the presence of migrated shear fluid in the working chamber. Such undesired clutch output engagement due to “morning sickness” can, for instance, produce a relatively high fan speed output (in fan clutch applications) with undesired fan noise, parasitic power losses, and excessive engine cooling. Although fluid in the working chamber due to “morning sickness” is generally pumped out of the working chamber to the reservoir quickly following a period of operation, it is desired to substantially avoid the “morning sickness” phenomenon entirely.
Therefore, it is desired to provide an alternative viscous clutch and/or valve system to address the “morning sickness” phenomenon.